1. Field of the Invention
The present invention relates to a malleolar implant for a partial or total prosthesis of the ankle and to an ancillary tool for placing such an implant.
2. Description of the Related Art
It is known, for example from EP-A-0 864 304, to fit an ankle prosthesis with a malleolar implant intended to bear against an articular surface at the level of the astragalus, whether it be question of a natural surface or of a surface of a prosthetic component. During an operation on an ankle, access to the internal articular surfaces is limited by the ligamentary system which does not necessarily allow a sufficient dislocation of the joint. In particular, access to the internal surface of the fibular malleolus may be insufficient, which induces difficulties in positioning the implant, particularly by impaction.
With reference to the embodiments of FIGS. 4 and 5, it is envisaged in EP-A-0 864 304 to introduce an implant from the outer face of the fibula. However, this necessarily limits the surface of the head of this implant, which must be less than or equal to the surface of the orifice provided in the bone, so that it is necessarily of relatively small dimensions with the result of substantially fragilizing the malleolus.
For the foregoing reasons, the positioning of the malleolar implants in the known prostheses is not entirely satisfactory.
It is a particular object of the present invention to overcome these drawbacks by proposing a novel malleolar implant which may be positioned precisely, even though access to the internal surface of the fibular malleolus may be limited and whereas its articular head presents dimensions allowing it to perform its function efficiently.
To that end, the invention relates to a malleolar implant comprising a head, intended to bear against the astragalus or an astragalian prosthetic component and a shank provided to be introduced in a bore in the fibula, characterized in that the shank is provided with means for hooking a traction member adapted to be maneuvered from the outer side of the fibula, in order to position the shank in the bore.
Thanks to the invention, the implant may be pre-positioned towards the inner face of the fibular malleolus and pulled through the through bore provided in the malleolus, with the result that the surgeon does not have to manipulate the implant with precision inside the joint, i.e. between the fibula and the tibia or between the fibula and the astragalus. The surgeon may exert an efficient effort on the traction member, which may be a flexible tie such as a suture thread, without being hindered by the surrounding bones. As a result, the positioning of the shank of the implant in the bore in the fibula may be precise, in particular due to the fact that the outer diameter of the shank may be substantially equal to the inner diameter of this bore, as the effort of traction which may be exerted from the outside of the fibula may be intense.
According to an advantageous aspect of the invention, the shank is provided with at least one orifice for passage of a flexible tie adapted to be engaged through the bore. In particular, the shank may comprise a plurality of orifices for passage of a flexible tie, such orifices being distributed over the length of this shank.
According to another advantageous aspect of the invention, the shank is provided with means for axial hold inside the bore. These means, which may be formed by outer radial flanges distributed over the length of the shank, make it possible efficiently to immobilize the shank inside the bore after it has been introduced therein by traction on the flexible member or tie.
The invention also relates to an ancillary tool for placing a malleolar implant as described hereinabove and, more specifically, a tool which comprises a spacer-block adapted to be inserted between the tibia and the astragalus of an ankle, and a lug fast with this spacer block and extending up to the vicinity of the outer surface of the fibular malleolus when the spacer block is in place between the tibia and the astragalus, this lug supporting a guide for boring the malleolus from its outer surface.
Thanks to the invention, the bore of the fibular malleolus may be effected from its outer surface and in the direction of its inner surface, with a determined relative positioning with respect to the tibia and the astragalus, with the result that the position of the malleolar implant in place in this bore is determined with precision with respect to the respective articular surfaces of the astragalus or of the tibia or of corresponding prosthetic components. The spacer block may be provided to cooperate with natural articular surfaces of the tibia and/or of the astragalus or with surfaces created by resection of these bones, in the case of placing a total ankle prosthesis.
According to an advantageous aspect of the invention, the spacer block is provided with a housing for receiving a shim of thickness adapted to the distance between the lower surface of the tibia and upper surface of the astragalus. This aspect of the invention makes it possible to maintain a distance corresponding to that which will be subsequently created by the prosthetic elements mounted in the lower part of the tibia and in the upper part of the astragalus, when the position of the malleolar implant is determined.
According to another advantageous aspect of the invention, the lug is articulated on the spacer block, with a limited possibility of pivoting. This makes it possible to adjust the position of the malleolus bore guide about the pivot axis of the lug with respect to the spacer block. In that case the spacer block and the lug are advantageously provided with orifices for passage of a common pivot pin.
It is also possible for the bore guide to be associated with a device for clamping the malleolus against a bearing surface formed on the lug or the spacer block. This allows a firm immobilization of the fibular malleolus during boring and thus ensures precision of the boring operation.